1. Technical Field
This invention relates to communications systems, in particular to those enabling automatic communications between a central station and a plurality of satellite stations.
2. Background Art
Data communications systems enabling connections to be automatically established, such as through commercial telephone systems, between a central data processing station and a plurality of satellite stations are well known. Such systems are totally oriented to central station control, wherein the central station controls the time at which a given satellite station communicates with the central station, controls the initiation and termination of all such communications, and controls the nature of such communications once established.
For example, U.S. Pat. No. 3,245,043 (Gaffney and Kusnick) is directed to a message communication system in which a plurality of widely spaced apart satellite stations are connected to a central data processing unit. In such a system, each satellite station includes means for storing information which is subsequently transmitted to the central station for processing. In that system, all satellite stations are serially connected, such that data from the most remote station flows through all closer satellite stations prior to being received by the central station. Each station is provided with a gate which senses the absence of signals from other satellite stations directed toward the central station, and thereupon pre-empts the transmission line in order to transmit signals stored within its own information store.
In U.S. Pat. No. 3,629,831 (Mikus and Harvey), an apparatus for controlling data transmissions between a central station and a plurality of satellite stations in which a data conversion unit is provided within the central station to enable data to be transmitted to and received from the satellite stations in serially encoded digital form, whereas it is communicated to a central data processor in parallel encoded digital form. In this system, a satellite station may request communication with the central station, whereupon a selecting means within the central station randomly detects that a given station is in condition to transmit data and thereupon controls the transmission and receipt of information transmitted from that satellite. In both of the systems noted above, a given satellite that is already connected to the central station precludes connection of other satellite stations to the central station such that all communications from other satellites, both of routine and priority type information, would be thwarted.
Other communications systems are also known which operate on a pure interrupt basis, that is, the occurrance of an alarm signal from a sensor associated with a satellite station immediately causes that satellite to activate automatic dialing equipment, thus securing an available transmission line for immediate transmission of that alarm signal to a central station.